Fertilizers Garden Myths

The Rusty Nail Myth

Rusty nails give nothing to plants… so why do gardeners keep adding them to their soil? Source: http://www.thetatoohut.com

Since time immemorial, gardeners having been adding rusty nails to the soil at the foot of their plants. By this trick of magic, they expect:

  • Blue spruces to be bluer;
  • Hydrangea to bloom better and/or have bluer flowers;
  • Fruit trees to produce more;
  • Oaks suffering from chlorosis (yellow leaves) to green up;
  • Plants to profit from an iron supplement;
  • Alkaline soils to become more acid;
  • And probably dozens of other effects.

And none of the above are true.

It’s easy enough  to understand the basic concept behind this myth. If a nail rusts, it’s because it contains iron and iron is one of the minerals that plants need to grow. And once people understand that iron is essential to plant growth, imaginations run wild.

The problem is that the iron produced by rusty nails is iron oxide, an essentially insoluble compound. Only a very tiny amount might theoretically be released by bacterial action. And very little of that will be absorbed by plants. So even if you fill the ground with rusty nails, it changes almost nothing for the plants nearby… but it does put you at risk of tetanus should ever you scratch yourself on a nail, rusty or not, when you garden in the sector.

At any rate, iron is an abundant element in nature and is rarely lacking in garden soil. It is also usually available in a sufficiently soluble form for plants to absorb it, at least when the soil’s pH is somewhat to highly acidic (below 7). If the soil is alkaline, however, (a pH of 7 or above), iron may be present, but fixed to soil particles in such a way that it is not available to plants. This will cause iron chlorosis (interveinal yellowing) in many plants.

20180908B www.pthomeandgarden.com
Iron chelate. Source: http://www.pthomeandgarden.com

When this occurs, however, rather than applying iron in the form of nails, you should first consider trying to reduce the soil’s pH, perhaps by sulfur applications or by mixing peat moss into the soil. Alternatively, you can spray a solution of iron sulphate directly onto the foliage (many plants readily absorb minerals through their leaves) or water the soil with a solution of iron chelate, which is a form of iron that is readily absorbed by plant roots. But in no way can rusty nails be more than marginally useful to plants.

And by the way, adding iron to the soil, even in a chelated form, will do nothing to make a blue spruce bluer. Its color is determined genetically and you can’t change it.

There is really no use whatsoever for rusty nails in gardening. Just don’t use them!

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

6 comments on “The Rusty Nail Myth

  1. Any thoughts on using laterite for this purpose? I have some dracaena and have been wanting to produce a potting medium that is more similar to the lateritic soil they naturally grow in out in the Madgascar rain forests.

    • Thoughts, yes. Proof of them? No!

      OK, I have a personal theory that plants that grow in extreme soils dont’t really need those conditions, but rather are just able to survive them. This gives them an advantage over neighboring plants and thus they can become a dominant part of the vegetation. Yet, most also grow in “better” soils and do just fine. The examples I’d use would be plants that grow in alkaline soils. Although many gardeners knock themselves out trying to make their soils just as alkaline as the plants had in the wild, they seem to grow perfectly well, and in fact, sometimes more vigorously, in soils with more “average” pH. It would certainly be an interesting test to see if dracaenas (not all of which are from Madagacar) do better with laterite added or not.

  2. A scratch from a nail has nothing to do with contracting Tetanus. Any scratch would be the same risk. A scratch from a rock or stick is the same risk. Tetanus is already in garden soil, especially if you add organic matter like manure s Tetanus grows in organic matter. Any scratch while working in the soil can expose the person to Tetanus. Most gardeners who get deep in the soil with their hands have been getting natural Tetanus boosters every season. The real Tetanus risk comes from penetrating puncture wounds like from a nail sticking out of a board that is stepped on and penetrates the skin, not a loose nail that only scratches the skin.

  3. In all due respect, I believe you are mistaken. Just because something is insoluble does not mean it cannot become soluble. There are many things in the soil that are processed by bacteria, microorganisms and enzymes that make things that were “unavailable” now “available” for uptake for the plant. This is why we all work so hard to improve the soil and have a plethora of bacteria and such processing things in the soil for better uptake of vitamins and minerals.

    Iron oxide is made soluble by oxalic acid which is already found in many plants. It seems plausible as these plants are mulched into the soil the oxalic acid is released in amounts that could contribute.

    • I added that comment due to a remark on what I though was a trustworthy web site. I’ll remove. It was, of course, neither here nor there: iron has nothing to do with blue foliage.

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